The present invention relates to a projection screen, particularly to a reflection-type screen for the projection of motion pictures in movies, projection-type televisions, and the like.
Screens for slide or OHP projections or projections of movies or videos generally comprise a laminate comprising a dark-color backing sheet and, laminated thereon, a white polyvinyl chloride sheet. Such screens reflect projected light in a homogeneous and isotropic manner in all directions, so that the homogeneity of the picture is high. However, the quantity of reflected light distributed in the vicinity of the direction of sight of an actual viewer is low, and the picture image is so dark that the projected image cannot be clearly viewed unless the room is darkened. On the other hand, there is a reflection-type screen using an aluminum reflecting plate having a roughened surface instead of the white sheet. In this screen, although the projected image can be clearly viewed in a bright room, since the screen is not flexible, it cannot be enclosed by winding.
A screen comprising a polyvinyl chloride sheet and reflective glass beads adhered thereto for the purpose of enhancing the reflectance and diffusion effect is known in the art. This screen, however, has a problem that the surface is uneven and likely to become contaminated and the glass beads are liable to peel off when dirt on the surface is wiped off. Further, the use of this type of screen as a wind-up screen causes the glass beads to unfavorably fall off when the screen is repeatedly wound up and unwound.
In connection with the screen comprising a dark-color backing sheet and a white polyvinyl chloride sheet, a technique is disclosed where a metallic deposit layer is provided as a reflecting layer on the polyvinyl chloride sheet, a translucent polyvinyl chloride sheet containing a pearl pigment is laminated on the reflecting layer and the surface of the laminate is embossed (see Japanese Utility Model Laid-Open No. 40835/1989).
The screen having a metallic reflecting layer has a problem that the light reflectance is so high that a halation occurs, which makes it difficult to view the projected image. Further, in the formation of the metallic deposit layer as the reflecting layer, the selection and pretreatment of the plastic sheet are important for facilitating the adhesion of the deposit layer. Polyester sheets, which are generally said to have a good adhesion to an aluminum deposit, are unfavorably liable to cause a fold mark. Specifically, the transportation or the repetition of winding/unwinding of the screen gives rise to a fold mark that is remarkably prominent due to its high light reflectance.
Further, when the whole layer comprises a soft material, such as a soft or semi-rigid polyvinyl chloride sheet, the stress created during winding/unwinding of the screen unfavorably gives rise to deformation such as elongation and sagging.
Japanese Patent Application 196763/1991 proposes a screen comprising a dimensionally stable ground fabric having on its back surface a light absorbing layer and, provided on the ground fabric in the following order, a white, opaque and soft plastic sheet and a light diffusing layer comprising a translucent and soft plastic and, incorporated into the plastic, a fine powder of a glitter or calcite, the screen having an embossed surface and a screen comprising a white, opaque and soft plastic substrate sheet having on its back surface a light absorbing layer and, provided on the substrate sheet, a light diffusing layer comprising a translucent and soft plastic and, incorporated into the plastic, a fine powder of a glitter or calcite, the screen having an embossed surface.
In this type of screen, it is difficult to form an exact fine uneven pattern on the surface of the screen due to a weave pattern of the glass ground fabric, uneven formation of the nonwoven fabric, etc., which renders the surface of the projection film uneven. This unfavorably gives rise to turbulence of the projected image or moire due to the interference of pixels with the uneven configurations, so that it is difficult to provide a configuration having stable optical properties.